The objective is the investigation of cyclic azo dioxides (diazene N, N-dioxides), a class of compounds of potential value as cancer chemotherapeutic agents. Of particular interest is the equilibrium connecting cyclic azo dioxides (polar, chemically unreactive species) with nitroso species (less polar and of moderate-to-high reactivity in several distinctive and potentially selective ways towards biological substrates. A major objective is the synthesis and study of a series of cyclic azo dioxides to assess the factors (steric, electronic, solvation) controlling the cyclic azo dioxide - bisnitroso equilibrium. Related objectives include studies of the reactivity of cyclic azo dioxides substituted by hydrogen and halogen at the alpha position. The alpha-hydrogen examples may permit the incorporation of the azo dioxide moiety in systems of biological interest by enolization and reaction with electrophilic sites, the alpha-halogen examples by ionization and reaction with nucleophilic sites. Further objectives are the investigation of cyclic azo dioxides with respect to oxygen transfer reactions and metal-complexing ability, and investigation of new systems isoelectronic with azo dioxides. The results of the studies will be used to select and prepare a series of cyclic azo dioxides for testing as cancer chemotherapeutic agents.